Interactions of Bacteria with the Mediterranean Fruit Fly

In a study supported by the BARD Fund, a team of US and Israeli scientists have gained new insight into the intricate relationship between the Mediterranean fruit fly – a major agricultural pest – and the bacteria that reside in its gut. Their findings may provide Agriculture with improved means of preventing this insect from damaging fruit.

The Mediterranean fruit fly, Ceratitis capitata, is a major agricultural pest. The female fly can lay her eggs in a wide variety of fruits; her offspring feed on the fruit, thereby ruining them. It is estimated that the worldwide financial loss due to the destructive activities of the Mediterranean fruit fly is $1 billion per year

The most common method for preventing the Mediterranean fruit fly from destroying fruit is the sterile insect technique (SIT). This method involves the release of a large number of sterile male flies in orchards. Female flies that mate with the sterile males lay sterile eggs. A drawback to this method, however, is the relative unattractiveness of the sterile males. Supported by the BARD Fund, the scientists have found that by manipulating the bacterial composition in the sterile flies’ gut in the laboratory, they can increase the male’s attractiveness to the female fly, thereby increasing the effectiveness of the sterile insect technique. The scientists’ research has further revealed that most of the microbes in the fly’s gut are Enterobacteriaceae, a large group of bacteria found in the digestive system of many animals. The researchers observed that the composition of this bacterial community, which is transmitted from the female fly to her progeny, changes as the fly develops. Interestingly, the researchers found that the Enterobacteriaceae similarly alter their support activities with each developmental stage. At the larval stage, which occurs in the fruit, many of the Enterobacteriaceae species are able to degrade fruit tissues and cause rotting. This activity may help provide nutrients to the growing larva. Moreover, these bacteria are able to convert atmospheric nitrogen, which the fly cannot use, into organic nitrogen, which the fly utilizes, for example, in the synthesis of amino acids, the building blocks of proteins. In the adult fly, in contrast, Enterobacteriaceae were found to affect the fly’s reproductive abilities. When the scientists inhibited the Enterobacteriaceae, the fly’s egg-laying rate decreased and, moreover, copulation was diminished. Another bacterial community that the team detected in the fly’s gut was Pseudomonas. They found that, although this microbe is present in the fly’s gut throughout the fly’s life cycle, its abundance remains very low. When the level of this bacterium in the fly’s gut was artificially increased, the flies rapidly died.

This understanding of the microbial ecology of the insect's gut microbiota now enables the scientist to go one step forward and upscale the experiments with SIT flies to more realistic settings modeling what happens in the field. This study can prove important in ameliorating medfly control in a relatively simple manner.